Enhancements to phase-noise compensation reference signal design and scrambling

ABSTRACT

Methods, systems, and devices for wireless communication are described. In one example, phase-noise compensation tracking signals (PTRS) may be transmitted using sets of resource blocks (RBs), where a frequency for each PTRS within the sets RBs is different from a frequency corresponding to a direct current (DC) tone. In another example, a time-domain-based PTRS may be used, where a discrete Fourier transform (DFT)-spread-orthogonal frequency division multiplexing (DFT-s-OFDM) symbol may include a cyclic prefix and a PTRS inserted in the DFT-s-OFDM symbol. Additionally or alternatively, a guard-interval-based DFT-s-OFDM symbol may include a PTRS that replaces part or all of a guard interval. In some examples, subsets of tones used for PTRS across a system bandwidth may be transmitted using a scrambled modulation symbol, where at least one antenna port may be used for the transmission of PTRS.

CROSS REFERENCES

This application is a continuation of U.S. patent application Ser. No.16/436,458, entitled “ENHANCEMENTS TO PHASE-NOISE COMPENSATION REFERENCESIGNAL DESIGN AND SCRAMBLING” and filed Jun. 10, 2019, which is acontinuation of U.S. patent application Ser. No. 15/707,821, entitled“ENHANCEMENTS TO PHASE-NOISE COMPENSATION REFERENCE SIGNAL DESIGN ANDSCRAMBLING” and filed Sep. 18, 2017, which claims priority to U.S.Provisional Patent Application No. 62/401,049, entitled “ENHANCEMENTS TOPHASE-NOISE COMPENSATION REFERENCE SIGNAL DESIGN AND SCRAMBLING” andfiled Sep. 28, 2016, assigned to the assignee hereof, and each of whichare hereby expressly incorporated by reference herein in their entirety.

INTRODUCTION

The following relates generally to wireless communication, and morespecifically to enhancements to phase-noise compensation referencesignal design and scrambling.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include fourth generation (4G) systems such as aLong Term Evolution (LTE) systems or LTE-Advanced (LTE-A) systems, andfifth generation (5G) systems which may be referred to as New Radio (NR)systems. These systems may employ technologies such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal frequency division multipleaccess (OFDMA), or discrete Fourier transform-spread-orthogonalfrequency division multiplexing (DFT-s-OFDM). A wireless multiple-accesscommunications system may include a number of base stations or networkaccess nodes, each simultaneously supporting communication for multiplecommunication devices, which may be otherwise known as user equipment(UE).

In some cases, transmissions in a wireless communications system may beimpacted by interference. As a result, a receiver, such as a UE, may usereference signals to mitigate interference. Depending on a location ofthe reference signals within wireless resources, however, a receiver maybe unable to efficiently receive the reference signals due tointerference with tones within the resources. Some receivers may be ableto use reference signals assigned to other receivers. However,transmitting additional information to enable this reference signalsharing may significantly increase scheduling overhead and createadditional problems. Thus, communication efficiency within the wirelesscommunications system may benefit from techniques that enable coherentscheduling of reference signals and improve flexibility for referencesignal reception at a receiver.

SUMMARY

A method of wireless communication is described. The method may includeidentifying a frequency corresponding to a direct current (DC) tonewithin a set of resource blocks, determining a frequency for each of oneor more phase-noise tracking reference signals (PTRS) based at least inpart on the DC tone, each determined frequency different from thefrequency corresponding to the DC tone, and transmitting the one or morePTRS using the set of resource blocks based at least in part on thedetermined frequency.

An apparatus for wireless communication is described. The apparatus mayinclude means for identifying a frequency corresponding to a DC tonewithin a set of resource blocks, means for determining a frequency foreach of one or more PTRS based at least in part on the DC tone, eachdetermined frequency different from the frequency corresponding to theDC tone, and means for transmitting the one or more PTRS using the setof resource blocks based at least in part on the determined frequency.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to identify a frequency correspondingto a DC tone within a set of resource blocks, determine a frequency foreach of one or more PTRS based at least in part on the DC tone, eachdetermined frequency different from the frequency corresponding to theDC tone, and transmit the one or more PTRS using the set of resourceblocks based at least in part on the determined frequency.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to identify a frequencycorresponding to a DC tone within a set of resource blocks, determine afrequency for each of one or more PTRS based at least in part on the DCtone, each determined frequency different from the frequencycorresponding to the DC tone, and transmit the one or more PTRS usingthe set of resource blocks based at least in part on the determinedfrequency.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for transmitting an indication of theidentified frequency corresponding to the DC tone.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying that a resource blockof the set of resource blocks overlaps with the DC tone, wherein the oneor more PTRS may be transmitted using one or more resource blocks of theset of resource blocks that may be different from the resource blockincluding the DC tone.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying that each resourceblock of the set of resource blocks includes at least some of the one ormore PTRS, wherein the determining may be based at least in part onidentifying that each resource block includes at least some of the oneor more PTRS.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying that a first resourceblock of the set of resource blocks overlaps with the DC tone, whereinthe determining comprises assigning at least some of the one or morePTRS to one or more frequencies of the first resource block.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the frequency corresponding toeach of the one or more PTRS may be based at least in part on a numberof component carriers, a system bandwidth, or both.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, a frequency density of thePTRS may be based at least in part on a number of resource blocks in theset of resource blocks.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a plurality of tonesacross the set of resource blocks different from the frequencycorresponding to the DC tone, the plurality of tones corresponding to aplurality of symbols across the set of resource blocks and associatedwith at least one antenna port. Some examples of the method, apparatus,and non-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for assigning afirst subset of the plurality of tones for data. Some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove may further include processes, features, means, or instructionsfor assigning a second subset of the plurality of tones for PTRS. Someexamples of the method, apparatus, and non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for scrambling a modulation symbol for each tone of thesecond subset. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for transmitting thefirst subset and the second subset using the scrambled modulationsymbols.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the transmitting comprisestransmitting the second subset using the at least one antenna port basedat least in part on a resource block assignment, the resource blockassignment comprising a number of layers used for data in the set ofresource blocks.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the second subset correspondsto an antenna port of the at least one antenna port. Some examples ofthe method, apparatus, and non-transitory computer-readable mediumdescribed above may further include processes, features, means, orinstructions for refraining from transmitting PTRS using the antennaport. Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for reassigning the second subset fordata or a vacant tone.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the second subset correspondsto an antenna port of the at least one antenna port and contains at mostone tone per resource block of the set of resource blocks. Some examplesof the method, apparatus, and non-transitory computer-readable mediumdescribed above may further include processes, features, means, orinstructions for assigning a third subset of the plurality of tones fora demodulation reference signal (DMRS), the third subset and the firstsubset overlapping partially, overlapping completely, or being disjoint,and the third subset corresponding to a group of antenna ports of the atleast one antenna port. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for transmitting thethird subset using the group of antenna ports, wherein the third subsetcomprises each of the at most one tone per resource block of the set ofresource blocks.

A method of wireless communication is described. The method may includegenerating a DFT-s-OFDM symbol, appending a PTRS to the generatedDFT-s-OFDM symbol, appending a cyclic prefix to the generated DFT-s-OFDMsymbol, and transmitting the generated DFT-s-OFDM symbol comprising thecyclic prefix and the PTRS.

An apparatus for wireless communication is described. The apparatus mayinclude means for generating a DFT-s-OFDM symbol, means for appending aPTRS to the generated DFT-s-OFDM symbol, means for appending a cyclicprefix to the generated DFT-s-OFDM symbol, and means for transmittingthe generated DFT-s-OFDM symbol comprising the cyclic prefix and thePTRS.

Another apparatus for wireless communication is described. The apparatusmay include a processor, memory in electronic communication with theprocessor, and instructions stored in the memory. The instructions maybe operable to cause the processor to generate a DFT-s-OFDM symbol,append a PTRS to the generated DFT-s-OFDM symbol, append a cyclic prefixto the generated DFT-s-OFDM symbol, and transmit the generatedDFT-s-OFDM symbol comprising the cyclic prefix and the PTRS.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions operable to cause a processor to generate a DFT-s-OFDMsymbol, append a PTRS to the generated DFT-s-OFDM symbol, append acyclic prefix to the generated DFT-s-OFDM symbol, and transmit thegenerated DFT-s-OFDM symbol comprising the cyclic prefix and the PTRS.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the cyclic prefix may beappended to the beginning of the generated DFT-s-OFDM symbol and thePTRS may be appended to a beginning of the cyclic prefix, to an end ofthe generated DFT-s-OFDM symbol, or a combination thereof.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, the generated DFT-s-OFDMsymbol comprises a guard interval, and wherein the appending the PTRS tothe generated DFT-s-OFDM symbol comprises replacing at least a portionof the guard interval with the PTRS.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for performing aweighted-overlap-and-add scheme within the generated DFT-s-OFDM symbolat a boundary between the generated DFT-s-OFDM symbol and the appendedPTRS.

In some examples of the method, apparatus, and non-transitorycomputer-readable medium described above, appending the PTRS to thegenerated DFT-s-OFDM symbol comprises assigning the PTRS to an input ofa discrete Fourier transform (DFT) spreading operation used to generatethe DFT-s-OFDM symbol. In some examples of the method, apparatus, andnon-transitory computer-readable medium described above, appending thePTRS to the generated DFT-s-OFDM symbol comprises appending the PTRS toan output of an inverse fast Fourier transform (IFFT) operation used togenerate the DFT-s-OFDM symbol.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for initializing the scrambling on aper-subframe basis or a per-symbol basis. In some examples of themethod, apparatus, and non-transitory computer-readable medium describedabove, the initializing may be based at least in part on a function of acell identifier, a subframe index, a symbol index, or a combinationthereof. Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for assigning scrambled modulationsymbols to the second subset based at least in part on an ordering of aport-index, a tone index, a symbol index, or a combination thereof.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining that a tone of thesecond subset may be unused for PTRS. Some examples of the method,apparatus, and non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions fordiscarding the modulation symbol corresponding to the tone based atleast in part on the determining. In some examples of the method,apparatus, and non-transitory computer-readable medium described above,the first subset or the second subset comprise vacant tones.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining a first scramblingsequence for a first receiver and a second scrambling sequence for asecond receiver. Some examples of the method, apparatus, andnon-transitory computer-readable medium described above may furtherinclude processes, features, means, or instructions for assigning thefirst scrambling sequence or the second scrambling sequence to one ormore tones of the second subset based at least in part on transmissionsintended for the first receiver or the second receiver.

Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for initializing the scrambling basedat least in part on receiver-specific information, the receiver-specificinformation comprising at least a radio network temporary identifier(RNTI). Some examples of the method, apparatus, and non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for mapping the modulation symbol ontoat least one tone of the second subset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example a wireless communications system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure;

FIG. 2 illustrates an example of a wireless communications system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure;

FIG. 3 illustrates an example of wireless resources in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure;

FIGS. 4A through 4D illustrate examples of DFT-s-OFDM symbolconfigurations in a system that supports enhancements to PTRS design andscrambling in accordance with one or more aspects of the presentdisclosure;

FIG. 5 illustrates an example of another DFT-s-OFDM symbol configurationin a system that supports enhancements to PTRS design and scrambling inaccordance with one or more aspects of the present disclosure;

FIGS. 6 through 9 illustrate examples of process flows in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure;

FIGS. 10 through 12 show block diagrams of a device that supportsenhancements to PTRS design and scrambling in accordance with one ormore aspects of the present disclosure;

FIG. 13 illustrates a block diagram of a system including a base stationthat supports enhancements to PTRS design and scrambling in accordancewith one or more aspects of the present disclosure; and

FIGS. 14 and 15 illustrate methods for enhancements to PTRS design andscrambling in accordance with one or more aspects of the presentdisclosure.

DETAILED DESCRIPTION

The described techniques relate to improved methods, systems, devices,and apparatuses that support enhancements to phase-noise compensationreference signals (PCRS) design and scrambling. Generally, the describedtechniques provide for identification of a DC tone, which may influencetransmissions of PCRS (e.g., which may alternatively be referred to asphase-noise tracking reference signals, phase tracking referencesignals, or PTRS). It is to be understood that, though described in thecontext or PTRS collision avoidance, the DC tone indication may be usedfor other purposes (e.g., multi-user scheduling) without deviating fromthe scope of the present disclosure.

As an example, transmitting PTRS to avoid collisions with the DC tonemay enable improved reception of PTRS by a base station or a UE. In oneexample, multiple PTRS may be transmitted using sets of resource blocks(RBs), where a frequency for each PTRS within the sets of RBs isdifferent from a frequency corresponding to a DC tone. In anotherexample, time-domain-based PTRS may be used, where a DFT-s-OFDM symbolmay include a cyclic prefix and a PTRS appended to a beginning or end ofthe DFT-s-OFDM symbol. In aspects, a DFT-s-OFDM symbol may alternativelybe referred to as a single-carrier frequency division multiplexing(SC-FDM) symbol. Additionally or alternatively, a guard-interval-basedDFT-s-OFDM symbol may include a PTRS that replaces part or all of aguard interval. The PTRS may be inserted either before or after theDFT-spreading operation. In some examples, subsets of tones used forPTRS across a system bandwidth may be transmitted using a scrambledmodulation symbol, where at least one antenna port may be used for thetransmission of PTRS.

In some wireless communications systems, phase noise may impactcommunications performance. Phase noise levels may increase with highercarrier frequencies, and wireless communications systems that use, forexample, carrier frequencies above 6 GHz, may thus be affected byincreasing phase noise. Accordingly, a reference signal, such as a PTRS,may be transmitted by a UE and used by a receiver (e.g., a base station)to estimate and correct the phase noise.

Wireless communications systems, such as orthogonal frequency divisionmultiplexing (OFDM) systems, may include transmissions of unmodulatedtones or subcarriers that are used by receiving devices to identify acenter frequency of transmitted wireless resources (e.g., a DC tone). Inaspects of the present disclosure, a UE may identify a DC tone for anuplink transmission and convey an indication of the DC tone to a targetbase station. For example, the UE may convey the DC tone location usingsemi-static signaling (e.g., RRC signaling or semi-static uplink controlsignaling). In some cases, the UE may avoid collisions with the DC tone(e.g., for DMRS and/or PTRS transmissions). For example, PTRStransmissions may collide with the DC tone, preventing receivers fromefficiently utilizing the PTRS for phase noise correction. That is, if afrequency for a PTRS (e.g., or a DMRS) is close to, or overlaps with, afrequency corresponding to a DC tone, then PTRS reception on thosefrequencies may be compromised by a DC offset within the receiver.

In some cases, PTRS transmissions may be scheduled on frequenciesdifferent from a frequency or frequencies that corresponds to a DC tone.That is, PTRS may be transmitted within wireless resources (e.g., RBs)using a design that avoids transmitting the PTRS on a same frequencythat corresponds to a DC tone. As a result, frequencies used for PTRStransmissions to a receiver may be based on the DC tone, and may avoidinterference caused by PTRS frequencies overlapping with the DC tone.

In some examples, scrambling of PTRS tones may be performed according todifferent schemes, such as a receiver-independent scheme and/or areceiver-specific scheme. In a receiver-independent scheme, even thoughPTRS transmissions may be directed at a specific receiver to help thatreceiver correct phase noise, a receiver may also use any PTRS that isscheduled or intended for other receivers. Accordingly, a scrambler maygenerate a scrambling modulation symbol for every possible PTRS toneacross a system bandwidth, enabling receivers to use PTRS that may bescheduled for different receivers. Additionally or alternatively, areceiver may not gain much from using PTRS sent to other receivers, andcontrol information may be to tailored for a PTRS scrambling to bespecific to a particular receiver and the receiver's assignment type.

Additionally, a waveform for DFT-s-OFDM may be configured to include atime-domain PTRS. For example, a DFT-s-OFDM symbol may be generated anda cyclic prefix may be appended, followed by a time domain PTRS insertedafter the addition of the cyclic prefix, at a start, an end, or both ofthe DFT-s-OFDM symbol. That is, pre-DFT or post-DFT insertion of PTRSfor an uplink DFT-s-OFDM symbol may be supported in accordance withtechniques described below.

Aspects of the disclosure are initially described in the context of awireless communications system. Further examples are then provided thatillustrate frequencies used for PTRS in addition to time-domain PTRStransmissions. Aspects of the disclosure are further illustrated by anddescribed with reference to apparatus diagrams, system diagrams, andflowcharts that relate to enhancements to PTRS design and scrambling.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with one or more aspects of the present disclosure. Thewireless communications system 100 includes base stations 105 (e.g.,gNodeBs (gNBs), and/or radio heads (RHs)), UEs 115, and a core network130. In some examples, the wireless communications system 100 may be aLTE network, a LTE-A network, or a NR network. In some cases, wirelesscommunications system 100 may support enhanced broadband communications,ultra-reliable (e.g., mission critical) communications, low latencycommunications, or communications with low-cost and low-complexitydevices.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Base stations 105 described herein mayinclude or may be referred to by those skilled in the art as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, an eNodeB (eNB), a next-generation Node B orgiga-nodeB (either of which may be referred to as a gNB), a Home NodeB,a Home eNodeB, or some other suitable terminology. Wirelesscommunications system 100 may include base stations 105 of differenttypes (e.g., macro or small cell base stations). The UEs 115 describedherein may be able to communicate with various types of base stations105 and network equipment including macro eNBs, small cell eNBs, gNBs,relay base stations, and the like.

Each base station 105 may be associated with a particular geographiccoverage area 110 in which communications with various UEs 115 issupported. Each base station 105 may provide communication coverage fora respective geographic coverage area 110 via communication links 125,and communication links 125 between a base station 105 and a UE 115 mayutilize one or more carriers. Communication links 125 shown in wirelesscommunications system 100 may include uplink transmissions from a UE 115to a base station 105, or downlink transmissions, from a base station105 to a UE 115. Downlink transmissions may also be called forward linktransmissions while uplink transmissions may also be called reverse linktransmissions.

The geographic coverage area 110 for a base station 105 may be dividedinto sectors making up only a portion of the geographic coverage area110, and each sector may be associated with a cell. For example, eachbase station 105 may provide communication coverage for a macro cell, asmall cell, a hot spot, or other types of cells, or various combinationsthereof. In some examples, a base station 105 may be movable andtherefore provide communication coverage for a moving geographiccoverage area 110. In some examples, different geographic coverage areas110 associated with different technologies may overlap, and overlappinggeographic coverage areas 110 associated with different technologies maybe supported by the same base station 105 or by different base stations105. The wireless communications system 100 may include, for example, aheterogeneous LTE/LTE-A or NR network in which different types of basestations 105 provide coverage for various geographic coverage areas 110.

The term “cell” refers to a logical communication entity used forcommunication with a base station 105 (e.g., over a carrier), and may beassociated with an identifier for distinguishing neighboring cells(e.g., a physical cell identifier (PCID), a virtual cell identifier(VCID)) operating via the same or a different carrier. In some examples,a carrier may support multiple cells, and different cells may beconfigured according to different protocol types (e.g., machine-typecommunication (MTC), narrowband Internet-of-Things (NB-IoT), enhancedmobile broadband (eMBB), or others) that may provide access fordifferent types of devices. In some cases, the term “cell” may refer toa portion of a geographic coverage area 110 (e.g., a sector) over whichthe logical entity operates.

UEs 115 may be dispersed throughout the wireless communications system100, and each UE 115 may be stationary or mobile. A UE 115 may also bereferred to as a mobile device, a wireless device, a remote device, ahandheld device, or a subscriber device, or some other suitableterminology, where the “device” may also be referred to as a unit, astation, a terminal, or a client. A UE 115 may also be a personalelectronic device such as a cellular phone, a personal digital assistant(PDA), a tablet computer, a laptop computer, or a personal computer. Insome examples, a UE 115 may also refer to a wireless local loop (WLL)station, an Internet of Things (IoT) device, an Internet of Everything(IoE) device, or an MTC device, or the like, which may be implemented invarious articles such as appliances, vehicles, meters, or the like. Insome cases, UEs 115 may be designed to support critical functions (e.g.,mission critical functions), and a wireless communications system 100may be configured to provide ultra-reliable communications for thesefunctions.

Some UEs 115, such as MTC or IoT devices, may be low cost or lowcomplexity devices, and may provide for automated communication betweenmachines (e.g., via Machine-to-Machine (M2M) communication). M2Mcommunication or MTC may refer to data communication technologies thatallow devices to communicate with one another or a base station 105without human intervention. In some examples, M2M communication or MTCmay include communications from devices that integrate sensors or metersto measure or capture information and relay that information to acentral server or application program that can make use of theinformation or present the information to humans interacting with theprogram or application. Some UEs 115 may be designed to collectinformation or enable automated behavior of machines. Examples ofapplications for MTC devices include smart metering, inventorymonitoring, water level monitoring, equipment monitoring, healthcaremonitoring, wildlife monitoring, weather and geological eventmonitoring, fleet management and tracking, remote security sensing,physical access control, and transaction-based business charging.

In some cases, a UE 115 may also be able to communicate directly withother UEs 115 (e.g., using a peer-to-peer (P2P) or device-to-device(D2D) protocol). One or more of a group of UEs 115 utilizing D2Dcommunications may be within the geographic coverage area 110 of a basestation 105. Other UEs 115 in such a group may be outside the geographiccoverage area 110 of a base station 105, or be otherwise unable toreceive transmissions from a base station 105. In some cases, groups ofUEs 115 communicating via D2D communications may utilize a one-to-many(1:M) system in which each UE 115 transmits to every other UE 115 in thegroup. In some cases, a base station 105 facilitates the scheduling ofresources for D2D communications. In other cases, D2D communications arecarried out between UEs 115 without the involvement of a base station105.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., via an S1 or otherinterface). Base stations 105 may communicate with one another overbackhaul links 134 (e.g., via an X2 or other interface) either directly(e.g., directly between base stations 105) or indirectly (e.g., via corenetwork 130).

The core network 130 may provide user authentication, accessauthorization, tracking, Internet Protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The core network 130 may be anevolved packet core (EPC), which may include at least one mobilitymanagement entity (MME), at least one serving gateway (S-GW), and atleast one Packet Data Network (PDN) gateway (P-GW). The MME may managenon-access stratum (e.g., control plane) functions such as mobility,authentication, and bearer management for UEs 115 served by basestations 105 associated with the EPC. User IP packets may be transferredthrough the S-GW, which itself may be connected to the P-GW. The P-GWmay provide IP address allocation as well as other functions. The P-GWmay be connected to the network operators IP services. The operators IPservices may include access to the Internet, Intranet(s), an IPMultimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service.

At least some of the network devices, such as base station 105 mayinclude subcomponents such as an access network entity 107, which may bean example of an access node controller (ANC). Each access networkentity 107 may communicate with a number of UEs 115 through a number ofother access network transmission entities 108, each of which may be anexample of a smart radio head, or a transmission/reception point (TRP).In some configurations, various functions of each access network entityor base station 105 may be distributed across various network devices(e.g., radio heads and access network controllers) or consolidated intoa single network device (e.g., a base station 105).

In some cases, wireless communications system 100 may be a packet-basednetwork that operate according to a layered protocol stack. In the userplane, communications at the bearer or Packet Data Convergence Protocol(PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may insome cases perform packet segmentation and reassembly to communicateover logical channels. A Medium Access Control (MAC) layer may performpriority handling and multiplexing of logical channels into transportchannels. The MAC layer may also use hybrid automatic repeat request(HARQ) to provide retransmission at the MAC layer to improve linkefficiency. In the control plane, the Radio Resource Control (RRC)protocol layer may provide establishment, configuration, and maintenanceof an RRC connection between a UE 115 and a base station 105 or corenetwork 130 supporting radio bearers for user plane data. At thePhysical (PHY) layer, transport channels may be mapped to physicalchannels.

In some cases, UEs 115 and base stations 105 may support retransmissionsof data to increase the likelihood that data is received successfully.HARQ feedback is one technique of increasing the likelihood that data isreceived correctly over a communication link 125. HARQ may include acombination of error detection (e.g., using a cyclic redundancy check(CRC)), forward error correction (FEC), and retransmission (e.g.,automatic repeat request (ARQ)). HARQ may improve throughput at the MAClayer in poor radio conditions (e.g., signal-to-noise conditions). Insome cases, a wireless device may support same-slot HARQ feedback, wherethe device may provide HARQ feedback in a specific slot for datareceived in a previous symbol in the slot. In other cases, the devicemay provide HARQ feedback in a subsequent slot, or according to someother time interval.

Time intervals in LTE or NR may be expressed in multiples of a basictime unit, which may, for example, refer to a sampling period ofT_(s)=1/30,720,000 seconds. Time intervals of a communications resourcemay be organized according to radio frames each having a duration of 10milliseconds (ms), where the frame period may be expressed asT_(f)=307,200 T. The radio frames may be identified by a system framenumber (SFN) ranging from 0 to 1023. Each frame may include 10 subframesnumbered from 0 to 9, and each subframe may have a duration of 1 ms. Asubframe may be further divided into 2 slots each having a duration of0.5 ms, and each slot may contain 6 or 7 modulation symbol periods(e.g., depending on the length of the cyclic prefix prepended to eachsymbol period). Excluding the cyclic prefix, each symbol period maycontain 2048 sampling periods. In some cases a subframe may be thesmallest scheduling unit of the wireless communications system 100, andmay be referred to as a transmission time interval (TTI). In othercases, a smallest scheduling unit of the wireless communications system100 may be shorter than a subframe or may be dynamically selected (e.g.,in bursts of shortened TTIs (sTTIs) or in selected component carriersusing sTTIs).

In some wireless communications systems, a slot may further be dividedinto multiple mini-slots containing one or more symbols. In someinstances, a symbol of a mini-slot or a mini-slot may be the smallestunit of scheduling. Each symbol may vary in duration depending on thesubcarrier spacing or frequency band of operation, for example. Further,some wireless communications systems may implement slot aggregation inwhich multiple slots or mini-slots are aggregated together and used forcommunication between a UE 115 and a base station 105.

The term “carrier” refers to a set of radio frequency spectrum resourceshaving a defined physical layer structure for supporting communicationsover a communication link 125. For example, a carrier of a communicationlink 125 may include a portion of a radio frequency spectrum band thatis operated according to physical layer channels for a given radioaccess technology. Each physical layer channel may carry user data,control information, or other signaling. A carrier may be associatedwith a pre-defined frequency channel (e.g., an E-UTRA absolute radiofrequency channel number (EARFCN)), and may be positioned according to achannel raster for discovery by UEs 115. Carriers may be downlink oruplink (e.g., in a frequency division duplexing (FDD) mode), or beconfigured to carry downlink and uplink communications (e.g., in a timedivision duplexing (TDD) mode). In some examples, signal waveformstransmitted over a carrier may be made up of multiple sub-carriers(e.g., using multi-carrier modulation (MCM) techniques such as OFDM orDFT-s-OFDM).

The organizational structure of the carriers may be different fordifferent radio access technologies (e.g., LTE, LTE-A, NR, etc.). Forexample, communications over a carrier may be organized according toTTIs or slots, each of which may include user data as well as controlinformation or signaling to support decoding the user data. A carriermay also include dedicated acquisition signaling (e.g., synchronizationsignals or system information, etc.) and control signaling thatcoordinates operation for the carrier. In some examples (e.g., in acarrier aggregation configuration), a carrier may also have acquisitionsignaling or control signaling that coordinates operations for othercarriers.

Physical channels may be multiplexed on a carrier according to varioustechniques. A physical control channel and a physical data channel maybe multiplexed on a downlink carrier, for example, using time divisionmultiplexing (TDM) techniques, frequency division multiplexing (FDM)techniques, or hybrid TDM-FDM techniques. In some examples, controlinformation transmitted in a physical control channel may be distributedbetween different control regions in a cascaded manner (e.g., between acommon control region or common search space and one or more UE-specificcontrol regions or UE-specific search spaces).

A carrier may be associated with a particular bandwidth of the radiofrequency spectrum, and in some examples the carrier bandwidth may bereferred to as a “system bandwidth” of the carrier or the wirelesscommunications system 100. For example, the carrier bandwidth may be oneof a number of predetermined bandwidths for carriers of a particularradio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz). Insome examples, each served UE 115 may be configured for operating overportions or all of the carrier bandwidth. In other examples, some UEs115 may be configured for operation using a narrowband protocol typethat is associated with a predefined portion or range (e.g., a set ofsubcarriers or RBs) within a carrier (e.g., “in-band” deployment of anarrowband protocol type).

In a system employing MCM techniques, a resource element may consist ofone symbol period (e.g., a duration of one modulation symbol) and onesubcarrier, where the symbol period and subcarrier spacing are inverselyrelated. The number of bits carried by each resource element may dependon the modulation scheme (e.g., the order of the modulation scheme).Thus, the more resource elements that a UE 115 receives and the higherthe order of the modulation scheme, the higher the data rate may be forthe UE 115. In multiple-input, multiple-output (MIMO) systems, awireless communications resource may refer to a combination of a radiofrequency spectrum resource, a time resource, and a spatial resource(e.g., spatial layers), and the use of multiple spatial layers mayfurther increase the data rate for communications with a UE 115.

Devices of the wireless communications system 100 (e.g., base stations105 or UEs 115) may have a hardware configuration that supportscommunications over a particular carrier bandwidth, or may beconfigurable to support communications over one of a set of carrierbandwidths. In some examples, the wireless communications system 100 mayinclude base stations 105 and/or UEs that can support simultaneouscommunications via carriers associated with more than one differentcarrier bandwidth.

Wireless communications system 100 may support communication with a UE115 on multiple cells or carriers, a feature which may be referred to ascarrier aggregation (CA) or multi-carrier operation. A UE 115 may beconfigured with multiple downlink CCs and one or more uplink CCsaccording to a carrier aggregation configuration. Carrier aggregationmay be used with both FDD and TDD component carriers.

In some cases, wireless communications system 100 may utilize enhancedcomponent carriers (eCCs). An eCC may be characterized by one or morefeatures including wider carrier or frequency channel bandwidth, shortersymbol duration, shorter TTI duration, or modified control channelconfiguration. In some cases, an eCC may be associated with a carrieraggregation configuration or a dual connectivity configuration (e.g.,when multiple serving cells have a suboptimal or non-ideal backhaullink). An eCC may also be configured for use in unlicensed spectrum orshared spectrum (e.g., where more than one operator is allowed to usethe spectrum). An eCC characterized by wide carrier bandwidth mayinclude one or more segments that may be utilized by UEs 115 that arenot capable of monitoring the whole carrier bandwidth or are otherwiseconfigured to use a limited carrier bandwidth (e.g., to conserve power).

In some cases, an eCC may utilize a different symbol duration than otherCCs, which may include use of a reduced symbol duration as compared withsymbol durations of the other CCs. A shorter symbol duration may beassociated with increased spacing between adjacent subcarriers. Adevice, such as a UE 115 or base station 105, utilizing eCCs maytransmit wideband signals (e.g., according to frequency channel orcarrier bandwidths of 20, 40, 60, 80 MHz, etc.) at reduced symboldurations (e.g., 16.67 microseconds). A TTI in eCC may consist of one ormultiple symbol periods. In some cases, the TTI duration (that is, thenumber of symbol periods in a TTI) may be variable.

Wireless communications system 100 may operate using one or morefrequency bands, typically in the range of 300 MHz to 300 GHz.Generally, the region from 300 MHz to 3 GHz is known as the ultra-highfrequency (UHF) region or decimeter band, since the wavelengths rangefrom approximately one decimeter to one meter in length. UHF waves maybe blocked or redirected by buildings and environmental features.However, the waves may penetrate structures sufficiently for a macrocell to provide service to UEs 115 located indoors. Transmission of UHFwaves may be associated with smaller antennas and shorter range (e.g.,less than 100 km) compared to transmission using the smaller frequenciesand longer waves of the high frequency (HF) or very high frequency (VHF)portion of the spectrum below 300 MHz.

Wireless communications system 100 may also operate in a super highfrequency (SHF) region using frequency bands from 3 GHz to 30 GHz, alsoknown as the centimeter band. The SHF region includes bands such as the5 GHz industrial, scientific, and medical (ISM) bands, which may be usedopportunistically by devices that can tolerate interference from otherusers.

Wireless communications system 100 may also operate in an extremely highfrequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz),also known as the millimeter band. In some examples, wirelesscommunications system 100 may support millimeter wave (mmW)communications between UEs 115 and base stations 105, and EHF antennasof the respective devices may be even smaller and more closely spacedthan UHF antennas. In some cases, this may facilitate use of antennaarrays within a UE 115. However, the propagation of EHF transmissionsmay be subject to even greater atmospheric attenuation and shorter rangethan SHF or UHF transmissions. Techniques disclosed herein may beemployed across transmissions that use one or more different frequencyregions, and designated use of bands across these frequency regions maydiffer by country or regulating body.

In some examples, base station 105 or UE 115 may be equipped withmultiple antennas, which may be used to employ techniques such astransmit diversity, receive diversity, MIMO communications, orbeamforming. For example, wireless communication system may use atransmission scheme between a transmitting device (e.g., a base station105) and a receiving device (e.g., a UE 115), where the transmittingdevice is equipped with multiple antennas and the receiving devices areequipped with one or more antennas. MIMO communications may employmultipath signal propagation to increase the spectral efficiency bytransmitting or receiving multiple signals via different spatial layers,which may be referred to as spatial multiplexing. The multiple signalsmay, for example, be transmitted by the transmitting device viadifferent antennas or different combinations of antennas. Likewise, themultiple signals may be received by the receiving device via differentantennas or different combinations of antennas. Each of the multiplesignals may be referred to as a separate spatial stream, and may carrybits associated with the same data stream (e.g., the same codeword) ordifferent data streams. Different spatial layers may be associated withdifferent antenna ports used for channel measurement and reporting. MIMOtechniques include single-user MIMO (SU-MIMO) where multiple spatiallayers are transmitted to the same receiving device, and multiple-userMIMO (MU-MIMO) where multiple spatial layers are transmitted to multipledevices.

Beamforming, which may also be referred to as spatial filtering,directional transmission, or directional reception, is a signalprocessing technique that may be used at a transmitting device or areceiving device (e.g., a base station 105 or a UE 115) to shape orsteer an antenna beam (e.g., a transmit beam or receive beam) along aspatial path between the transmitting device and the receiving device.Beamforming may be achieved by combining the signals communicated viaantenna elements of an antenna array such that signals propagating atparticular orientations with respect to an antenna array experienceconstructive interference while others experience destructiveinterference. The adjustment of signals communicated via the antennaelements may include a transmitting device or a receiving deviceapplying certain amplitude and phase offsets to signals carried via eachof the antenna elements associated with the device. The adjustmentsassociated with each of the antenna elements may be defined by abeamforming weight set associated with a particular orientation (e.g.,with respect to the antenna array of the transmitting device orreceiving device, or with respect to some other orientation).

In some cases, wireless communications system 100 may utilize bothlicensed and unlicensed radio frequency spectrum bands. For example,wireless communications system 100 may employ License Assisted Access(LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technologyin an unlicensed band such as the 5 GHz ISM band. When operating inunlicensed radio frequency spectrum bands, wireless devices such as basestations 105 and UEs 115 may employ listen-before-talk (LBT) proceduresto ensure a frequency channel is clear before transmitting data. In somecases, operations in unlicensed bands may be based on a CA configurationin conjunction with CCs operating in a licensed band (e.g., LAA).Operations in unlicensed spectrum may include downlink transmissions,uplink transmissions, peer-to-peer transmissions, or a combination ofthese. Duplexing in unlicensed spectrum may be based on FDD, TDD, or acombination of both.

Wireless communications systems such as an NR system may utilize anycombination of licensed, shared, and unlicensed spectrum bands, amongothers. The flexibility of eCC symbol duration and subcarrier spacingmay allow for the use of eCC across multiple spectrums. In someexamples, NR shared spectrum may increase spectrum utilization andspectral efficiency, specifically through dynamic vertical (e.g., acrossfrequency) and horizontal (e.g., across time) sharing of resources.

Some UEs 115 may be configured to employ operating modes that reducepower consumption, such as half-duplex communications (e.g., a mode thatsupports one-way communication via transmission or reception, but nottransmission and reception simultaneously). In some examples half-duplexcommunications may be performed at a reduced peak rate. Other powerconservation techniques for UEs 115 include entering a power saving“deep sleep” mode (e.g., or idle mode) when not engaging in activecommunications, or operating over a limited bandwidth (e.g., accordingto narrowband communications).

Devices operating in a shared or unlicensed frequency spectrum mayperform a clear channel assessment (CCA) prior to communicating in orderto determine whether the channel is available. A CCA may include anenergy detection procedure to determine whether there are any otheractive transmissions. For example, the device may infer that a change ina reference signal strength indication (RSSI) of a power meter indicatesthat a channel is occupied. Specifically, signal power is that isconcentrated in a certain bandwidth and exceeds a predetermined noisefloor may indicate another wireless transmitter. A CCA may also includedetection of specific sequences that indicate use of the channel. Forexample, another device may transmit a specific preamble prior totransmitting a data sequence. UEs 115 and base stations 105 operating inlicensed or unlicensed spectrum may transmit discovery reference signals(DRS) to convey information for identifying or establishing a radioconnection (e.g., or to facilitate fast transmission of a small cellfrom a low-power state to an active state).

A reference signal (RS) may be a signal, known to a receiving device,that is inserted into a transmitted signal in order to facilitatechannel estimation for coherent de-modulation and measurements. In thedownlink, cell-specific RSs may be available to all UEs 115 in a cell;UE-specific RSs may be embedded in the data for specific UEs 115; andmultimedia broadcast single frequency network (MBSFN)-specific RSs maybe provided in case of MBSFN operation. These RSs may occupy specifiedresource element (REs) within an OFDM symbol. In some cases, wirelesscommunications using OFDM may make use of a DC subcarrier, referred toherein as a DC tone. The DC tone may be a tone that is unmodulated, andmay be used by a receiving device to locate the center of an OFDMfrequency band. For example, the DC tone may occupy the center tone of72 active subcarriers transmitted by a base station 105 to a UE 115.

In some cases, a base station 105 may have prioritized access to atransmission medium within a discovery measurement timing configuration(DMTC) window of its cell. For example, in a CCA-exempt transmission(CET) scheme, a base station 105 may protect its DMTC window using asemi-persistent channel reservation signal. In this scheme, the basestation 105 may perform listen-before-talk at power up (e.g., when thecell transissions from a dormant mode to an active mode) and operateusing CET thereafter. LBT may be required if periodic transmission ofthe semi-persistent channel reservation signal is interrupted.Accordingly, aspects of a CET DMTC deployment may resemble operations ofa cell within a licensed spectrum. If CET is enabled, a base station 105associated with a first operator may protect the DMTC window of a basestation 105 associated with another operator (e.g., as described withreference to FIG. 3). In some cases, the DMTC windows of base stations105 belonging to the same network may be coordinated (e.g., maysubstantially overlap). Alternatively, in a non-CET deployment, the basestation may perform a CCA (e.g., using a single, omni-directionalsignal) before transmitting DRS.

Wireless communications system 100 may enable transmissions of PTRS thatenable improved reception of PTRS by receiving devices, such as a UE115. In one example, multiple PTRS may be transmitted using sets of RBs,where a frequency for each PTRS within the sets RBs is different from afrequency corresponding to a DC tone. In another example, atime-domain-based PTRS may be used, where a DFT-s-OFDM symbol mayinclude a cyclic prefix and a PTRS appended to a beginning or end of theDFT-s-OFDM symbol. Additionally or alternatively, a guard-interval-basedDFT-s-OFDM symbol may include a PTRS that replaces part or all of aguard interval, where the replacement may be performed either before(i.e., pre-DFT) or after (i.e., post-DFT) the DFT-spreading operation.In some examples, subsets of tones used for PTRS across a systembandwidth may be transmitted using a scrambled modulation symbol, whereat least one antenna port may be used for the transmission of PTRS.

One or more of base stations 105 may include a base stationcommunications manager 101. Similarly UEs 115 may include a UEcommunications manager 102. Base station communications manager 101and/or UE communications manager may identify a frequency correspondingto a DC tone within a set of resource blocks and transmit an indicationof the identified frequency corresponding to the DC tone. In some cases,one or both of the communications managers may determine a frequency foreach of one or more PTRS based at least in part on the DC tone, whereeach determined frequency is different from the frequency correspondingto the DC tone. One or both of the communications managers may transmitthe one or more PTRS using the set of resource blocks based at least inpart on the determined frequency. Transmitting the PTRS may includegenerating a DFT-s-OFDM symbol, appending a cyclic prefix to the symbol,appending a PTRS to the symbol, and transmitting the symbol comprisingthe PTRS and the cyclic prefix.

FIG. 2 illustrates an example of wireless communications system 200 forenhancements to PTRS design and scrambling in accordance with one ormore aspects of the present disclosure. Wireless communications system200 may include a base station 105-a, and UEs 115-a, 115-b, each ofwhich may be an example of the corresponding device as described withreference to FIG. 1. Wireless communications system 200 may enablereceivers to efficiently receive PTRS 205 for phase noise correction.Though aspects of the following are described with reference to downlinktransmissions, it is to be understood that the described techniques(e.g., or analogous techniques) may be extended to uplink transmissionswithout deviating from the scope of the present disclosure.

In wireless communications system 200, phase noise may have an impact oncommunications performance. Phase noise levels may increase with highercarrier frequencies, and the use of, for example, carrier frequenciesabove 6 GHz may thus be affected by relatively more phase noise.Accordingly, PTRS 205, may be transmitted by base station 105-a and usedby a receiver (e.g., UE 115-a and/or UE 115-b) to estimate and correctthe phase noise. Alternatively, PTRS 205 may be transmitted by UE 115-aand/or UE 115-b and used by base station 105-a to estimate and correctphase noise. As an example, PTRS 205 may be transmitted on a certainsubset of tones (e.g., frequencies) assigned to UE 115-a and in allsymbols (e.g., OFDM symbols) of a subframe. That is, PTRS 205-a may beassigned to UE 115-a, and PTRS 205-b may be assigned to UE 115-b.

A UE 115 (e.g., or a base station 105) may correct for phase noise bytracking a variation in a received signal at these tones over successivesymbols. In some cases, different tones may be used for differentantenna ports, and tone locations within a set of resources (e.g., anRB) may be fixed. As an example, if an RB includes 12 tones, indexed 0through 11, then each RB carrying PTRS may carry PTRS at tone indexes 3and 5, with tone 3 associated with a first antenna port (e.g., port 0)and tone 5 associated with a second antenna port (e.g., port 1).

Wireless communications system 200, may include transmissions ofunmodulated tones or subcarriers that are used by UEs 115 to identify acenter frequency of transmitted wireless resources (e.g., a DC tone).However, PTRS 205 may collide with the DC tone, preventing receiversfrom efficiently utilizing PTRS 205 for phase noise correction. Forexample, if a frequency for a PTRS 205-a is close to, or overlaps with,a frequency corresponding to a DC tone, then PTRS 205-a reception onthose frequencies may be compromised by a DC offset within a receivingdevice.

In some cases, PTRS 205 transmissions may be scheduled on frequenciesthat are different from a frequency that corresponds to a DC tone. Forexample, UEs 115-a, 115-b may provide an indication of a DC tone to basestation 105-a such that base station 105-a schedules the respective PTRS305 on frequencies that do not conflict with the respective DC tones.Generally, the PTRS 205 tone locations may be based at least in part ona RB assignment. In one example, RBs used for PTRS 205 transmissions maybe chosen to exclude the DC tone, such as when PTRS 205 is sparselytransmitted over multiple RBs (e.g., PTRS 205 may only be present in oneof every four RBs). For example, in some cases the PTRS 205 frequencydensity (i.e., the number of tones carrying PTRS 205 in a given portionof a frequency spectrum) may be inversely proportional to the number ofRBs scheduled to carry PTRS 205. That is, PTRS 205 may be sparselytransmitted over multiple RBs when a larger number of RBs are scheduledto carry PTRS 205. Similarly, the PTRS 205 time density (i.e., thenumber of OFDM symbols in a subframe carrying PTRS 205) may be directlyproportional to the modulation and coding scheme (MCS). That is, thehigher MCS, the higher the PTRS 205 time density.

In another example, the frequencies used for PTRS 205 within each RB ofa set of RBs may be chosen to exclude the DC tone, even if PTRS 205 ispresent in every RB. Additionally or alternatively, differentfrequencies for PTRS 205 may be used only for RBs that overlap with theDC tone, such as when the placement of PTRS 205 frequencies for RBs thatare relatively far from the DC tone may be limiting. In some cases, thefrequency corresponding to the DC tone, relative to RBs which may beused for PTRS 205 assignment, may be a function of system information,such as the number of component carriers. An avoidance scheme, e.g.,different PTRS 205 locations for RBs containing or overlapping with theDC tone, may also be a function of the system information.

Scrambling of PTRS 205 may be performed according to different schemes,such as a receiver-independent scheme and a receiver-specific scheme. Ina receiver-independent scheme, even though PTRS 205 transmissions may bedirected at a specific receiver (e.g., PTRS 205-a assigned to UE 115-a)to help that receiver correct phase noise, a receiver (e.g., UE 115-b)may also use PTRS 205-a (i.e., a PTRS 205 that is scheduled or intendedfor other receivers).

For example, phase compensation may be implemented by tracking anevolution of phase noise across successive symbols, where the evolutionof phase noise may be independent of a tone index, and UE 115-a mayaccordingly use PTRS 205-b sent to UE 115-b. In some cases, absolutephases of the PTRS tones sent to different receivers in a same symbolmay not be combined in a meaningful way at any one receiver, since apropagation channel and beamforming/precoding on the channels may bedifferent. However, a variation of this phase across time (i.e., acrossOFDM symbols) may be the same on different tones, and may be combined.

For a UE 115 to use PTRS 205 sent to other receivers, the UE 115 mayneed to know the structure of those PTRS 205 transmissions, such aswhich tones are occupied by PTRS 205, the scrambling pattern, etc.However, overhead associated with communicating this information aboutother receivers can be prohibitively large. Thus, the tone locations andscrambling pattern may be designed to be independent of the receiver.For instance, UE 115-a may perform energy detection on tones notassigned to UE 115-a to determine whether those tones carry data for UE115-b. If energy is detected, UE 115-a may then exploit the known andreceiver-independent PTRS 205-b structure. In some cases, this may beperformed for tones assigned to the receiver, prior to decoding controlinformation that indicates the assigned tones.

In some cases, a PTRS 205 sent to a receiver may not be present on allantenna ports. That is, a number of antenna ports carrying PTRS 205 maybe less than a number of antenna ports carrying data, such that thephase noise for a group of data antenna ports may be tracked using aPTRS 205 of a single antenna port. In some cases, antenna ports carryingdata may additionally carry DMRS (e.g., which may be used to facilitatedemodulation of the data). Accordingly, the number of antenna portscarrying PTRS 205 may also be less than the number of antenna portscarrying DMRS. For example, port 0 may contain PTRS 205 while ports 0and 1 (e.g., or 1 and 2) may contain DMRS. That is, DMRS ports may bearranged in groups (e.g., ports 1 and 2 may form a DMRS port group), anda given PTRS port (e.g., port 0 or port 1) may be associated with theDMRS port group. In some cases, an antenna port may carry both PTRS andDMRS; alternatively, an antenna port may carry PTRS or DMRS (e.g., butnot both). Multiple such DMRS port groups may be formed, with each DMRSport group having an associated PTRS port. For example, a PTRS port maybe mapped onto a subcarrier along with one or more DMRS ports of itsassociated DMRS port group.

In some cases, tones that may be used for PTRS 205 and correspond to theunused antenna ports may be either unused (e.g., vacant tones) or maycarry data to the receiver. If the tones are unused, the receiver mayperform a PTRS 205 energy detection separately for each port using PTRStones not assigned to the receiver. If the tones carry data, then thereceiver may not be able to distinguish data from PTRS 205 on the tonesnot assigned to it, unless information about the other receivers isavailable (which may be prohibitive due to additional signaling). Insome examples, if a minimum set of tones/ports are known to alwayscontain PTRS 205, then tones in the set may be used by the receiver,even if the tones are assigned to other receivers. For example,precoding may be used such that transmissions associated with port 0 maybe the strongest (e.g., based on a signal-to-noise ratio (SNR)), and mayalways contain PTRS 205, where port 1 may or may not contain PTRS 205depending on other factors, such as a receiver assignment. In suchcases, port 0 PTRS tones directed to other users may be used by areceiver.

A receiver-independent PTRS scrambling scheme described above may beperformed to improve the flexibility of a receiver to receive and usePTRS 205 for phase noise correction. In such cases, a scrambler maygenerate a scrambling modulation symbol for every possible PTRS toneacross a system bandwidth, from every antenna port in every symbol,regardless of whether the tones may be used to carry PTRS 205, data, oris left vacant (e.g., based on which receiver the tone is assigned to).In some cases, receivers that use a subset of the system bandwidth maybe informed (e.g., through system information block (SIB) messages)about the whole system bandwidth. Accordingly, such receivers may enablethe scrambler to generate and discard a correct number of symbolscorresponding to PTRS 205 for the portion of the system bandwidth thatthe receivers do not use.

In some cases, the scrambler may be initialized on a per-subframe orper-symbol basis. Additionally, an initialization seed may be a functionof a cell identifier (ID), a subframe index, or a symbol index. In someexamples, the initialization seed may not be a function ofreceiver-specific information (such as a radio network temporaryidentifier (RNTI) or a receiver's tone/RB assignment). In some cases, anoutput of the scrambler output (e.g., a modulation symbol) may beassigned to possible PTRS tones following an ordering of a port index, afrequency (tone) index, and a symbol index. As an example, for each OFDMsymbol, the scrambler output may be assigned using an increasing toneindex for port 0, then for port 1, and so on. In some cases, differentports may use a same scrambling, or the ports may alternatively usedifferent scrambling to reduce a peak-to-average power ratio (PAPR)increase when precoding is applied. Additionally or alternatively, asame scrambling may be used on all OFDM symbols within a subframe. Insome cases, a scrambler output associated with a possible PTRS tone maybe discarded if that PTRS tone is not used to carry PTRS 205 (e.g., leftvacant, used to carry data, etc.).

In some cases, UE 115-a may not benefit from using PTRS 205-b sent to UE115-b, because PTRS 205-b may be received at a relatively low SNR. As anexample, PTRS 205-b may be transmitted in a radio frequency rangeassociated with directional transmissions to overcome pathloss, such aswith transmissions using mmW spectrum, where PTRS 205-b may be sent frombase station 105-a with different beamforming weighting from signalsintended for UE 115-a (e.g., PTRS 205-a). In some cases, UE 115-a mayhave to decode control information and determine the tones/RBs assignedto the UE 115-a. Accordingly, this control information may also be usedto tailor a PTRS scrambling to be specific to a particular receiver andthe receiver's assignment type. In such receiver-specific scramblingschemes, a descrambling generator at the receiver may not have togenerate outputs that will be subsequently discarded.

In such receiver-specific PTRS scrambling schemes, a scrambler mayscramble modulation symbols only for tones that are designated to carryPTRS 205. The scrambler may be initialized on a per-subframe orper-symbol basis, and an initialization seed may be a function ofcell-ID, subframe index, symbol index, and/or receiver-specificinformation (such as an RNTI or receiver's tone/RB assignment). Ascrambler output may be populated onto PTRS tones, following an orderingrule, such as described above for the receiver-independent schemes.Additionally, every scrambler output may be used, since the scrambleroutputs may be directly mapped to a specific PTRS tone, and may not bediscarded.

FIG. 3 illustrates an example of wireless resources 300 in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure. Wireless resources 300may illustrate an example of determining frequencies for PTRStransmissions that do not overlap with a DC tone. As described above, itis to be understood that though PTRS transmissions are used for the sakeof example, the described techniques may extend to other referencesignals as well (e.g., DMRS).

Wireless resources 300 may include a number of RBs 305, that include anumber of subcarriers 310 transmitted over a number of symbols 315.Subcarriers 310 may be used for, or may be associated with,transmissions by different antenna ports, and subcarrier locationswithin RB 305 may be fixed. As an example, an RB 305 may include 12subcarriers 310 (tones), indexed 0 through 11, and each RB 305 may carryPTRS 320 at tone indexes 3 and 5, with tone 3 associated with a firstantenna port (e.g., port 0) and tone 5 associated with a second antennaport (e.g., port 1).

In some cases, RBs 305 used for PTRS transmissions may be chosen toexclude a DC tone 325 (e.g., an unmodulated tone used by a receiver toidentify a center frequency of wireless resources 300). For example, aPTRS 320 may not be transmitted in each RB 305 assigned to a receiver,and any RBs 305 that do not include (or do not overlap with) the DC tone325, may be chosen to carry PTRS 320. In some cases, a UE 115 mayindicate a location of the DC tone 325 to a transmitting device (e.g., abase station 105) to facilitate efficient transmission of PTRS 320 or toprovide other benefits to the communications system.

In another example, the frequencies used for PTRS 320 within each RB 305of a set of RBs 305 may be chosen to exclude the DC tone 325, even ifPTRS 320 is present in every RB 305. That is, when DC tone 325 ispresent in an RB 305, the frequencies corresponding with PTRS 320 may bedifferent from the frequencies corresponding to DC tone 325.Additionally or alternatively, different frequencies for PTRS 320 may beused only for RBs 305 that overlap with the DC tone 325. For instance,wireless resources may include multiple RBs 305, and only an RB 305 thatoverlaps with DC tone 325 may include PTRS 320 on frequencies that aredifferent from DC tone 325. Accordingly, PTRS 320 may only betransmitted in the RB 305 that overlaps with DC tone 325 (e.g., shouldtransmitting PTRS 320 in other RBs 305 be limiting in any way), wherethe other RBs 305 may be relatively farther away from DC tone 325.

FIGS. 4A through 4D illustrate examples of DFT-s-OFDM symbolconfigurations 401 through 404 in a system that supports enhancements toPTRS design and scrambling in accordance with one or more aspects of thepresent disclosure. In some cases, a DFT-s-OFDM waveform may begenerated by using a frequency-contiguous tone assignment and performinga DFT operation on input modulation symbols prior to assigning thesymbols to tones. In aspects of the present disclosure, a DFT-s-OFDMwaveform may support pre-DFT PTRS insertion. Additionally, PTRS may betransmitted using additional tones besides those populated from the DFToutput. The additional tones may be placed adjacent to data tones, orinterspersed between the data tones.

A PTRS sequence transmitted in the time domain may be desirable. PTRSsequences in accordance with one or more of the described DFT-s-OFDMsymbol configurations 401 through 404 may improve system performance forwireless communications systems in which phase noise changes rapidly.The described configurations may apply to wireless communicationssystems associated with directional transmissions in which a high orderMCS is used (e.g., such that dynamic and accurate correction ofphase-noise may improve decoding of such symbols). That is, DFT-s-OFDMconfigurations 401 through 404 may enable phase-noise correction on aper-symbol basis (or some other suitable time interval), which may, forexample, be especially useful in the case of data transmissions that aresent using a high order MCS (e.g., in high SNR environments).

In the illustrative example provided in FIG. 4A, DFT-s-OFDM symbol 405-amay be generated by a transmitting device, and cyclic prefix 415-a maybe subsequently appended at the beginning of DFT-s-OFDM symbol 405-a.Additionally, PTRS 420-a may be appended at a beginning of cyclic prefix415-a. Additionally or alternatively, a PTRS may be appended to the endof a DFT-s-OFDM symbol. For instance, in the example provided in FIG.4B, DFT-s-OFDM symbol 405-b may be generated, and cyclic prefix 415-bmay be subsequently appended at the beginning of DFT-s-OFDM symbol405-b. Additionally, PTRS 420-b may be appended at an end of DFT-s-OFDMsymbol 405-b.

In the example provided in FIG. 4C, a PTRS 420-c may be appended to thebeginning and the end of a DFT-s-OFDM symbol 405-c. For instance,DFT-s-OFDM symbol 405-c may be generated, and cyclic prefix 415-c may besubsequently appended at the beginning of DFT-s-OFDM symbol 405-c. PTRS420-c may then be appended at a beginning of cyclic prefix 415-c, andPTRS 420-d may be appended at the end of DFT-s-OFDM symbol 405-c.

In the example provided in FIG. 4D, a PTRS 420-e is inserted at multiplepoints within the DFT-s-OFDM symbol 405-d. For instance, DFT-s-OFDMsymbol 405-d may be generated, and cyclic prefix 415-d may besubsequently appended at the beginning of DFT-s-OFDM symbol 405-d. PTRS420-e may be inserted at multiple points within the DFT-s-OFDM symbol405-d (e.g., in addition to or instead of appending the PTRS to thebeginning and/or end of the symbol). For example, such insertion may beachieved by inserting the PTRS prior to the DFT spreading operation(e.g., as described with reference to FIG. 6). For example, the PTRS420-e may be segmented and the various segments may be mapped to inputpositions of the DFT spreading operation to generate the DFT-s-OFDMsymbol 405-d.

In some examples, a weighted-overlap-and-add (WOLA) scheme may be usedbetween successive DFT-s-OFDM symbols. For example, multiple symbolsaccording to DFT-s-OFDM symbol configurations 401, 402, 403, and/or 404may be transmitted, where a WOLA scheme may be used between consecutiveDFT-s-OFDM symbols. Additionally, the WOLA scheme may be used during theappending of the PTRS 420 to the DFT-s-OFDM symbols 405 with cyclicprefix 415, as described above.

FIG. 5 illustrates an example of an DFT-s-OFDM symbol configuration 500for enhancements to PTRS design and scrambling in accordance with one ormore aspects of the present disclosure. DFT-s-OFDM symbol configuration500 may be an example of a guard-interval-based DFT-s-OFDM symbol usedfor transmission of PTRS.

Some wireless communications systems may use a guard-interval basedDFT-s-OFDM symbol, such as DFT-s-OFDM symbol 505, where zeros areincluded at the beginning and/or at the end of an input to aDFT-spreading operation. Accordingly, a time-domain DFT-s-OFDM symbolwaveform may have a low amplitude at the beginning and/or at the end.Such time-domain blanking may serve as a replacement for a cyclicprefix, and the blank period, or a portion of it, may also be replacedby a fixed, non-zero, time-domain waveform that may serve as atime-domain PTRS 520. However, this scheme may not allow for a system inwhich some receivers use OFDM waveforms (e.g., including a cyclicprefix) and other receivers use DFT-s-OFDM waveforms (e.g., including aguard-interval, but no cyclic prefix).

DFT-s-OFDM symbol configuration 500 may include the retention of cyclicprefix 515 and further introduces a PTRS 520 (e.g., a time-domain PTRS).For example, a guard interval-based DFT-s-OFDM symbol 505 may begenerated in the time domain using zero-insertion, DFT-spreading, andinverse fast Fourier transform (IFFT), where DFT-s-OFDM symbolconfiguration 500 includes guard period 510. Subsequently, part or allof the guard period 510 may be replaced with PTRS 520. In some cases,should PTRS 520 only occupy a portion of guard period 510, a portion 525of guard period 510 may remain.

In such cases, the resulting composite time-domain waveform may betreated as a single DFT-s-OFDM symbol prior to insertion of a cyclicprefix 515, where the cyclic prefix 515 may be appended to theDFT-s-OFDM symbol 505 and the guard period 510 (e.g., including the PTRS520). In one example, PTRS 520 may be inserted after an addition ofcyclic prefix 515, or may be inserted at a start or end (or both) ofDFT-s-OFDM symbol 505. In some cases, appending PTRS 520 may optionallybe accomplished using a WOLA scheme at an insertion point.

FIG. 6 illustrates an example of a process flow 600 that supportsenhancements to PTRS design and scrambling in accordance with one ormore aspects of the present disclosure. Process flow 600 may beperformed by a wireless device (e.g., a UE 115 or a base station 105).At 605, the wireless device may generate a PTRS. As illustrated by 610,the PTRS may in some cases serve as an input to a DFT spreadingoperation at 615 (e.g., which may be referred to as pre-DFT insertion).Alternatively the PTRS may be inserted after the DFT spreading operation(e.g., which may be referred to as post-DFT insertion). For example, asillustrated by 620, the PTRS may be appended in the frequency domain(e.g., following the DFT spreading operation at 615 but preceding theOFDM IFFT operation at 625). In another example, as illustrated by 630,the PTRS may be appended to the DFT-s-OFDM symbol generated by the OFDMIFFT operation at 625. At 635, the wireless device may append a CP, andat 640 the wireless device may optionally perform WOLA.

FIG. 7 illustrates an example of a process flow 700 in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure. Process flow 700 includesa UE 115-c and a base station 105-b, which may be examples of thecorresponding devices described with reference to FIGS. 1 and 2. Processflow 700 may illustrate the transmission of PTRS on frequencies that donot overlap with a DC tone.

At 705, UE 115-c may identify a frequency corresponding to a DC tonewithin a set of RB s. In some cases, UE 115-c may transmit an indicationof the identified frequency corresponding to the DC tone to base station105-b at 710. For example, the indication may be conveyed via uplinkcontrol signaling, RRC signaling, or some other semi-static signaling.In aspects, the identified DC tone may affect various communicationparameters. For example, the identified DC tone may impact the locationof PTRS (e.g., or other reference signals such as DMRS as describedabove), scheduling decisions made by base station 105-b, etc. In somecases, the DC tone location may change (e.g., based on UEimplementation). For example, when an additional component carrier isadded (e.g., or dropped), the DC tone location may change such thatthere may be a mechanism (e.g., a configuration message) to indicate thechange in DC tone location.

At 715, UE 115-c may identify that a subset of the set of RBs includesat least some of the one or more PTRS. In some cases, UE 115-c mayidentify that each RB of the set of RBs includes at least some of theone or more PTRS, and may assign the one or more PTRS to a frequency ofeach RB that is different from the frequency corresponding to the DCtone. Additionally or alternatively, UE 115-c may identify that acertain RB of the set of RBs overlaps with the DC tone, and may assignthe one or more PTRS to a frequency of the identified RB that isdifferent from the frequency corresponding to the DC tone. In somecases, the frequency corresponding to each of the one or more PTRS isbased at least in part on a number of component carriers, a systembandwidth, or both. For example, a PTRS may be transmitted in a systemusing carrier aggregation, and the frequency chosen for PTRStransmission may be based on respective resources used for a primary andsecondary component carrier.

At 720, UE 115-c may determine a frequency for each of one or more PTRSbased at least in part on the DC tone, where the determined frequency isdifferent from the frequency corresponding to the DC tone. In someexamples, UE 115-c may optionally transmit an indication of theidentified DC tone to base station 105-b at 720. In such cases, basestation 105-b may use the indication to identify the DC tone withinresources transmitted by UE 115-c.

At 725, UE 115-c may transmit, and base station 105-b may receive, theone or more PTRS using the set of RBs based at least in part on thedetermined frequency. In some cases, the one or more PTRS may betransmitted using one or more RBs that are different from a RB includingthe DC tone. At 730, base station 105-b may perform phase noisecorrection based at least in part on one or more received PTRS.

FIG. 8 illustrates an example of a process flow 800 in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure. Process flow 800 includesa UE 115-d and a base station 105-c, which may be examples of thecorresponding devices described with reference to FIGS. 1 and 2. Processflow 800 may illustrate an example of appending a PTRS to an DFT-s-OFDMsymbol.

At 805, UE 115-d may generate a DFT-s-OFDM symbol. In some examples, thegenerated DFT-s-OFDM symbol may include a guard interval. At 810, UE115-d may append a cyclic prefix to the generated DFT-s-OFDM symbolfollowed by appending a PTRS at 815. In some cases, the cyclic prefix isappended to the beginning of the generated DFT-s-OFDM symbol and thePTRS is appended to a beginning of the cyclic prefix, to an end of thegenerated DFT-s-OFDM symbol, or a combination thereof. In some examples,appending the PTRS to the generated DFT-s-OFDM symbol includes replacingat least a portion of the guard interval with the PTRS.

At 820, UE 115-d may optionally perform a WOLA scheme for a secondDFT-s-OFDM symbol associated with the generated DFT-s-OFDM symbol, thesecond DFT-s-OFDM symbol including a second cyclic prefix and a secondPTRS. For example, UE 115-d may generate multiple DFT-s-OFDM symbols asdescribe above, and may perform the WOLA scheme at a boundary betweenthe DFT-s-OFDM symbols. Additionally or alternatively, the WOLA schememay be performed within the generated DFT-s-OFDM symbol at a boundarybetween the generated DFT-s-OFDM symbol and the appended PTRS. In someexamples, the WOLA scheme may be performed both within the DFT-s-OFDMsymbols and between subsequent symbols. At 825, UE 115-d may transmit,and base station 105-c may receive, the generated DFT-s-OFDM symbolincluding the cyclic prefix and the PTRS. It is to be understood thatthough aspects of the preceding example are described with reference touplink transmissions, in some cases analogous techniques may be extendedto downlink transmissions without deviating from the scope of thepresent disclosure.

FIG. 9 illustrates an example of a process flow 900 in a system thatsupports enhancements to PTRS design and scrambling in accordance withone or more aspects of the present disclosure. Process flow 900 includesa UE 115-e and a base station 105-d, which may be examples of thecorresponding devices described with reference to FIGS. 1 and 2. Processflow 900 may illustrate an example of scrambling modulation symbolsacross a system bandwidth for the transmission of PTRS.

At 905, UE 115-e may identify multiple tones across a system bandwidth(e.g., or a set of RBs), where the tones correspond to multiple symbolsacross the system bandwidth and are associated with at least one antennaport. At 910, base station UE 115-e may assign a first subset of thetones for data. At 915, base station UE 115-e may assign a second subsetof the tones for PTRS. In some cases, the second subset corresponds toan antenna port of the at least one antenna port. In some cases, UE115-e may assign modulation symbols to the second subset based at leastin part on an ordering of a port-index, a tone index, a symbol index, ora combination thereof. In some cases, the first subset or the secondsubset include one or more vacant tones.

At 920, base station UE 115-e may scramble a modulation symbol for eachtone of the second subset. In some cases, the scrambling may beinitialized on a per-subframe basis or a per-symbol basis, and theinitializing may be based on a function of a cell identifier, a subframeindex, a symbol index, or a combination thereof.

At 925, base station UE 115-e may transmit, and base station 105-d mayreceive, the first subset and the second subset using the scrambledmodulation symbols. In some cases, transmitting the modulation symbolmay include transmitting the second subset using the at least on antennaport based at least in part on a RB assignment, the RB assignmentincluding at least a number of layers used for data in a RB. At 930,base station 105-d may perform phase noise correction based at least inpart on the received PTRS associated with the scrambled modulationsymbols. It is to be understood that though aspects of the precedingexample are described with reference to uplink transmissions, in somecases analogous techniques may be extended to downlink transmissionswithout deviating from the scope of the present disclosure.

FIG. 10 shows a block diagram 1000 of a wireless device 1005 thatsupports enhancements to phase-noise compensation reference signaldesign and scrambling in accordance with aspects of the presentdisclosure. Wireless device 1005 may be an example of aspects of a UE115 or a base station 105 as described herein. Wireless device 1005 mayinclude receiver 1010, communications manager 1015, and transmitter1020. Wireless device 1005 may also include a processor. Each of thesecomponents may be in communication with one another (e.g., via one ormore buses).

Receiver 1010 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to enhancementsto phase-noise compensation reference signal design and scrambling,etc.). Information may be passed on to other components of the device.The receiver 1010 may be an example of aspects of the transceiver 1335described with reference to FIG. 13. The receiver 1010 may utilize asingle antenna or a set of antennas.

Communications manager 1015 may be an example of aspects of thecommunications manager 1315 described with reference to FIG. 13.Communications manager 1015 and/or at least some of its varioussub-components may be implemented in hardware, software executed by aprocessor, firmware, or any combination thereof. If implemented insoftware executed by a processor, the functions of the communicationsmanager 1015 and/or at least some of its various sub-components may beexecuted by a general-purpose processor, a digital signal processor(DSP), an application-specific integrated circuit (ASIC), anfield-programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described in thepresent disclosure.

The communications manager 1015 and/or at least some of its varioussub-components may be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations by one or more physical devices. In someexamples, communications manager 1015 and/or at least some of itsvarious sub-components may be a separate and distinct component inaccordance with various aspects of the present disclosure. In otherexamples, communications manager 1015 and/or at least some of itsvarious sub-components may be combined with one or more other hardwarecomponents, including but not limited to an I/O component, atransceiver, a network server, another computing device, one or moreother components described in the present disclosure, or a combinationthereof in accordance with various aspects of the present disclosure.

Communications manager 1015 may identify a frequency corresponding to aDC tone within a set of resource blocks. Communications manager 1015 maydetermine a frequency for each of one or more PTRS based at least inpart on the DC tone, each determined frequency different from thefrequency corresponding to the DC tone. Communications manager 1015 maytransmit the one or more PTRS using the set of resource blocks based atleast in part on the determined frequency. The communications manager1015 may also generate a DFT-s-OFDM symbol, append a cyclic prefix tothe generated DFT-s-OFDM symbol, append a PTRS to the generatedDFT-s-OFDM symbol, and transmit the generated DFT-s-OFDM symbolincluding the cyclic prefix and the PTRS.

Transmitter 1020 may transmit signals generated by other components ofthe device. In some examples, the transmitter 1020 may be collocatedwith a receiver 1010 in a transceiver module. For example, thetransmitter 1020 may be an example of aspects of the transceiver 1335described with reference to FIG. 13. The transmitter 1020 may utilize asingle antenna or a set of antennas.

FIG. 11 shows a block diagram 1100 of a wireless device 1105 thatsupports enhancements to phase-noise compensation reference signaldesign and scrambling in accordance with aspects of the presentdisclosure. Wireless device 1105 may be an example of aspects of awireless device 1005 or a UE 115 or a base station 105 as described withreference to FIG. 10. Wireless device 1105 may include receiver 1110,communications manager 1115, and transmitter 1120. Wireless device 1105may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

Receiver 1110 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to enhancementsto phase-noise compensation reference signal design and scrambling,etc.). Information may be passed on to other components of the device.The receiver 1110 may be an example of aspects of the transceiver 1335described with reference to FIG. 13. The receiver 1110 may utilize asingle antenna or a set of antennas.

Communications manager 1115 may be an example of aspects of thecommunications manager 1315 described with reference to FIG. 13.Communications manager 1115 may also include DC tone component 1125,PTRS component 1130, DFT-s-OFDM symbol manager 1135, tone manager 1140,and scrambler 1145.

DC tone component 1125 may identify a frequency corresponding to a DCtone within a set of resource blocks and transmit an indication of theidentified frequency corresponding to the DC tone. DC tone component1125 may identify that a resource block of the set of resource blocksoverlaps with the DC tone, where the one or more PTRS are transmittedusing one or more resource blocks of the set of resource blocks that aredifferent from the resource block including the DC tone. DC tonecomponent 1125 may identify that a first resource block of the set ofresource blocks overlaps with the DC tone, where the determiningincludes assigning at least some of the one or more PTRS to one or morefrequencies of the first resource block

PTRS component 1130 may determine a frequency for each of one or morePTRS based on the DC tone, each determined frequency different from thefrequency corresponding to the DC tone. PTRS component 1130 may append aPTRS to the generated DFT-s-OFDM symbol. PTRS component 1130 may assignthe one or more PTRS to a frequency of each RB that is different fromthe frequency corresponding to the DC tone. PTRS component 1130 maytransmit the one or more PTRS using the set of resource blocks based onthe determined frequency. In some cases, the frequency corresponding toeach of the one or more PTRS is based on a number of component carriers,a system bandwidth, or both. PTRS component 1130 may determine that atone of the second subset is unused for PTRS, and discard the modulationsymbol corresponding to the tone based on the determining. PTRScomponent 1130 may identify that each resource block of the set ofresource blocks includes at least some of the one or more PTRS, wherethe determining is based on identifying that each resource blockincludes at least some of the one or more PTRS. In some cases, afrequency density of the PTRS is based on a number of resource blocks inthe set of resource blocks.

DFT-s-OFDM symbol manager 1135 may generate a DFT-s-OFDM symbol andappend a cyclic prefix to the generated DFT-s-OFDM symbol. In somecases, the cyclic prefix is appended to the beginning of the generatedDFT-s-OFDM symbol and the PTRS is appended to a beginning of the cyclicprefix, to an end of the generated DFT-s-OFDM symbol, or a combinationthereof. In some cases, the generated DFT-s-OFDM symbol includes a guardinterval, and appending the PTRS to the generated DFT-s-OFDM symbolincludes replacing at least a portion of the guard interval with thePTRS. The replacing may be performed either before or after theDFT-spreading operation. For example, the guard interval itself may becreated by insertion of zeroes at the beginning and/or end of the inputto the DFT-spreading operation. Pre-DFT PTRS insertion may correspond toreplacing some or all of these zeros with the PTRS signal (e.g., suchthat pre-DFT insertion may generally place PTRS at some subset of theinputs to the DFT-spreading operation). Alternatively, DFT-s-OFDM symbolmanager 1135 may append the PTRS to an output of an IFFT OFDM operation(e.g., prior to appending a cyclic prefix). DFT-s-OFDM symbol manager1135 may perform a weighted-overlap-and-add scheme for a secondDFT-s-OFDM symbol associated with the generated DFT-s-OFDM symbol, thesecond DFT-s-OFDM symbol including a second cyclic prefix and a secondPTRS. DFT-s-OFDM symbol manager 1135 may transmit the generatedDFT-s-OFDM symbol including the cyclic prefix and the PTRS. In somecases, the PTRS may be inserted before a DFT spreading operation used togenerate the DFT-s-OFDM symbol; alternatively, the PTRS may be insertedafter an IFFT operation used to generate the DFT-s-OFDM symbol.

Tone manager 1140 may identify a set of tones across the set of resourceblocks different from the frequency corresponding to the DC tone, theset of tones corresponding to a set of symbols across the set ofresource blocks and associated with at least one antenna port. Tonemanager 1140 may assign a first subset of the set of tones for data andmay assign a second subset of the set of tones for PTRS. In some cases,tone manager 1140 may reassign the second subset for data or a vacanttone and assign the modulation symbols to the second subset based on anordering of a port-index, a tone index, a symbol index, or a combinationthereof. In some cases, the second subset corresponds to an antenna portof the at least one antenna port. In some cases, the first subset or thesecond subset include vacant tones. In some cases, tone manager 1140 mayassign a third subset of the plurality of tones for DMRS, wherein thethird subset and the first subset overlap partially, completely, or notat all (e.g., being disjoint). In some cases, the third subsetcorresponds to a group of antenna ports of the at least one antenna portdifferent from the first antenna port. Tone manager 1140 may transmitthe first subset and the second subset using the scrambled modulationsymbols. In some cases, the transmitting includes transmitting thesecond subset using the at least one antenna port based on a resourceblock assignment, the resource block assignment including a number oflayers used for data in the set of resource blocks. In some cases, thefirst subset of tones may be associated with a group of antenna portsand the second subset of tones may be associated with a single antennaport, where each antenna port of the group of antenna ports isassociated with the single antenna port (e.g., each antenna port of thegroup of antenna ports may apply PTRS from the single antenna port totrack phase noise). In some cases, the second subset contains at mostone tone per resource block of the set of resource blocks. Tone manager1140 may transmit the third subset using the group of antenna ports,where the third subset includes each of the at most one tone perresource block of the set of resource blocks.

Scrambler 1145 may scramble a modulation symbol for each tone of thesecond subset, initialize the scrambling on a per-subframe basis or aper-symbol basis, and determine a first scrambling sequence for a firstreceiver and a second scrambling sequence for a second receiver. In someexamples, scrambler 1145 may assign the first scrambling sequence or thesecond scrambling sequence to one or more tones of the second subsetbased on transmissions intended for the first receiver or the secondreceiver and initialize the scrambling based on receiver-specificinformation, the receiver-specific information including at least aRNTI. In some cases, the initializing is based on a function of a cellidentifier, a subframe index, a symbol index, or a combination thereof.

Transmitter 1120 may transmit signals generated by other components ofthe device. In some examples, the transmitter 1120 may be collocatedwith a receiver 1110 in a transceiver module. For example, thetransmitter 1120 may be an example of aspects of the transceiver 1335described with reference to FIG. 13. The transmitter 1120 may utilize asingle antenna or a set of antennas.

FIG. 12 shows a block diagram 1200 of a communications manager 1215 thatsupports enhancements to phase-noise compensation reference signaldesign and scrambling in accordance with aspects of the presentdisclosure. The communications manager 1215 may be an example of aspectsof a communications manager 1015, a communications manager 1115, or acommunications manager 1315 described with reference to FIGS. 10, 11,and 13. The communications manager 1215 may include DC tone component1220, PTRS component 1225, DFT-s-OFDM symbol manager 1230, tone manager1235, and scrambler 1240. Each of these modules may communicate,directly or indirectly, with one another (e.g., via one or more buses).

DC tone component 1220 may identify a frequency corresponding to a DCtone within a set of resource blocks and transmit an indication of theidentified frequency corresponding to the DC tone. DC tone component1220 may identify that a resource block of the set of resource blocksoverlaps with the DC tone, where the one or more PTRS are transmittedusing one or more resource blocks of the set of resource blocks that aredifferent from the resource block including the DC tone. DC tonecomponent 1220 may identify that a first resource block of the set ofresource blocks overlaps with the DC tone, where the determiningincludes assigning at least some of the one or more PTRS to one or morefrequencies of the first resource block

PTRS component 1225 may determine a frequency for each of one or morePTRS based on the DC tone, each determined frequency different from thefrequency corresponding to the DC tone. PTRS component 1225 may append aPTRS to the generated DFT-s-OFDM symbol. PTRS component 1225 may assignthe one or more PTRS to a frequency of each RB that is different fromthe frequency corresponding to the DC tone. PTRS component 1225 maytransmit the one or more PTRS using the set of resource blocks based onthe determined frequency. In some cases, the frequency corresponding toeach of the one or more PTRS is based on a number of component carriers,a system bandwidth, or both. PTRS component 1225 may determine that atone of the second subset is unused for PTRS, and discard the modulationsymbol corresponding to the tone based on the determining. PTRScomponent 1225 may identify that each resource block of the set ofresource blocks includes at least some of the one or more PTRS, wherethe determining is based on identifying that each resource blockincludes at least some of the one or more PTRS. In some cases, afrequency density of the PTRS is based on a number of resource blocks inthe set of resource blocks.

DFT-s-OFDM symbol manager 1230 may generate a DFT-s-OFDM symbol andappend a cyclic prefix to the generated DFT-s-OFDM symbol. In somecases, the cyclic prefix is appended to the beginning of the generatedDFT-s-OFDM symbol and the PTRS is appended to a beginning of the cyclicprefix, to an end of the generated DFT-s-OFDM symbol, or a combinationthereof. In some cases, the generated DFT-s-OFDM symbol includes a guardinterval, and appending the PTRS to the generated DFT-s-OFDM symbolincludes replacing at least a portion of the guard interval with thePTRS. Alternatively, DFT-s-OFDM symbol manager 1230 may append the PTRSto an output of an IFFT OFDM operation (e.g., prior to appending acyclic prefix). DFT-s-OFDM symbol manager 1230 may perform aweighted-overlap-and-add scheme for a second DFT-s-OFDM symbolassociated with the generated DFT-s-OFDM symbol, the second DFT-s-OFDMsymbol including a second cyclic prefix and a second PTRS. DFT-s-OFDMsymbol manager 1230 may transmit the generated DFT-s-OFDM symbolincluding the cyclic prefix and the PTRS. In some cases, the PTRS may beinserted before a DFT spreading operation used to generate theDFT-s-OFDM symbol; alternatively, the PTRS may be inserted after an IFFToperation used to generate the DFT-s-OFDM symbol.

Tone manager 1235 may identify a set of tones across the set of resourceblocks different from the frequency corresponding to the DC tone, theset of tones corresponding to a set of symbols across the set ofresource blocks and associated with at least one antenna port. Tonemanager 1235 may assign a first subset of the set of tones for data andmay assign a second subset of the set of tones for PTRS. In some cases,tone manager 1235 may reassign the second subset for data or a vacanttone and assign the modulation symbols to the second subset based on anordering of a port-index, a tone index, a symbol index, or a combinationthereof. In some cases, the second subset corresponds to an antenna portof the at least one antenna port. In some cases, the first subset or thesecond subset include vacant tones. In some cases, tone manager 1235 mayassign a third subset of the plurality of tones for DMRS, wherein thethird subset and the first subset overlap partially, completely, or notat all (e.g., being disjoint). In some cases, the third subsetcorresponds to a group of antenna ports of the at least one antenna portdifferent from the first antenna port. Tone manager 1235 may transmitthe first subset and the second subset using the scrambled modulationsymbols. In some cases, the transmitting includes transmitting thesecond subset using the at least one antenna port based on a resourceblock assignment, the resource block assignment including a number oflayers used for data in the set of resource blocks. In some cases, thefirst subset of tones may be associated with a group of antenna portsand the second subset of tones may be associated with a single antennaport, where each antenna port of the group of antenna ports isassociated with the single antenna port (e.g., each antenna port of thegroup of antenna ports may apply PTRS from the single antenna port totrack phase noise). In some cases, the second subset contains at mostone tone per resource block of the set of resource blocks. Tone manager1235 may transmit the third subset using the group of antenna ports,where the third subset includes each of the at most one tone perresource block of the set of resource blocks.

Scrambler 1240 may scramble a modulation symbol for each tone of thesecond subset, initialize the scrambling on a per-subframe basis or aper-symbol basis, and determine a first scrambling sequence for a firstreceiver and a second scrambling sequence for a second receiver. In someexamples, scrambler 1240 may assign the first scrambling sequence or thesecond scrambling sequence to one or more tones of the second subsetbased on transmissions intended for the first receiver or the secondreceiver and initialize the scrambling based on receiver-specificinformation, the receiver-specific information including at least aRNTI. In some cases, the initializing is based on a function of a cellidentifier, a subframe index, a symbol index, or a combination thereof.

FIG. 13 shows a diagram of a system 1300 including a device 1305 thatsupports enhancements to phase-noise compensation reference signaldesign and scrambling in accordance with aspects of the presentdisclosure. Device 1305 may be an example of or include the componentsof wireless device 1005, wireless device 1105, or a UE 115 or a basestation 105 as described above, e.g., with reference to FIGS. 10 and 11.Device 1305 may include components for bi-directional voice and datacommunications including components for transmitting and receivingcommunications, including communications manager 1315, processor 1320,memory 1325, software 1330, transceiver 1335, antenna 1340, and I/Ocontroller 1345. These components may be in electronic communication viaone or more buses (e.g., bus 1310).

Processor 1320 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a central processing unit (CPU), amicrocontroller, an ASIC, an FPGA, a programmable logic device, adiscrete gate or transistor logic component, a discrete hardwarecomponent, or any combination thereof). In some cases, processor 1320may be configured to operate a memory array using a memory controller.In other cases, a memory controller may be integrated into processor1320. Processor 1320 may be configured to execute computer-readableinstructions stored in a memory to perform various functions (e.g.,functions or tasks supporting enhancements to phase-noise compensationreference signal design and scrambling).

Memory 1325 may include random access memory (RAM) and read only memory(ROM). The memory 1325 may store computer-readable, computer-executablesoftware 1330 including instructions that, when executed, cause theprocessor to perform various functions described herein. In some cases,the memory 1325 may contain, among other things, a basic input/outputsystem (BIOS) which may control basic hardware or software operationsuch as the interaction with peripheral components or devices.

Software 1330 may include code to implement aspects of the presentdisclosure, including code to support enhancements to phase-noisecompensation reference signal design and scrambling. Software 1330 maybe stored in a non-transitory computer-readable medium such as systemmemory or other memory. In some cases, the software 1330 may not bedirectly executable by the processor but may cause a computer (e.g.,when compiled and executed) to perform functions described herein.

Transceiver 1335 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1335 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1335 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas. In some cases, thewireless device may include a single antenna 1340. However, in somecases the device may have more than one antenna 1340, which may becapable of concurrently transmitting or receiving multiple wirelesstransmissions.

I/O controller 1345 may manage input and output signals for device 1305.I/O controller 1345 may also manage peripherals not integrated intodevice 1305. In some cases, I/O controller 1345 may represent a physicalconnection or port to an external peripheral. In some cases, I/Ocontroller 1345 may utilize an operating system such as iOS®, ANDROID®,MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operatingsystem. In other cases, I/O controller 1345 may represent or interactwith a modem, a keyboard, a mouse, a touchscreen, or a similar device.In some cases, I/O controller 1345 may be implemented as part of aprocessor. In some cases, a user may interact with device 1305 via I/Ocontroller 1345 or via hardware components controlled by I/O controller1345.

FIG. 14 shows a flowchart illustrating a method 1400 for enhancements tophase-noise compensation reference signal design and scrambling inaccordance with aspects of the present disclosure. The operations ofmethod 1400 may be implemented by a UE 115 or a base station 105 or itscomponents as described herein. For example, the operations of method1400 may be performed by a communications manager as described withreference to FIGS. 10 through 13. In some examples, a UE 115 or a basestation 105 may execute a set of codes to control the functionalelements of the device to perform the functions described below.Additionally or alternatively, the UE 115 or a base station 105 mayperform aspects of the functions described below using special-purposehardware.

At 1405 the UE 115 or a base station 105 may identify a frequencycorresponding to a DC tone within a set of resource s. The operations of1405 may be performed according to the methods described herein. Incertain examples, aspects of the operations of 1405 may be performed bya DC tone component as described with reference to FIGS. 10 through 13.

At 1410 the UE 115 or a base station 105 determine a frequency for eachof one or more PTRS (e.g., or some other applicable reference signal)based at least in part on the DC tone, each determined frequencydifferent from the frequency corresponding to the DC tone. Theoperations of 1410 may be performed according to the methods describedherein. In certain examples, aspects of the operations of 1410 may beperformed by a DC tone component as described with reference to FIGS. 10through 13.

At 1415 the UE 115 or a base station 105 may transmit the one or morePTRS using the set of resource s based at least in part on thedetermined frequency. The operations of 1415 may be performed accordingto the methods described herein. In certain examples, aspects of theoperations of 1415 may be performed by a PTRS component as describedwith reference to FIGS. 10 through 13.

FIG. 15 shows a flowchart illustrating a method 1500 for enhancements tophase-noise compensation reference signal design and scrambling inaccordance with aspects of the present disclosure. The operations ofmethod 1500 may be implemented by a UE 115 or a base station 105 or itscomponents as described herein. For example, the operations of method1500 may be performed by a communications manager as described withreference to FIGS. 10 through 13. In some examples, a UE 115 or a basestation 105 may execute a set of codes to control the functionalelements of the device to perform the functions described below.Additionally or alternatively, the UE 115 or a base station 105 mayperform aspects of the functions described below using special-purposehardware.

At 1505 the UE 115 or a base station 105 may generate a DFT-s-OFDMsymbol. The operations of 1505 may be performed according to the methodsdescribed herein. In certain examples, aspects of the operations of 1505may be performed by a DFT-s-OFDM symbol manager as described withreference to FIGS. 10 through 13.

At 1510 the UE 115 or a base station 105 may append a cyclic prefix tothe generated DFT-s-OFDM symbol. The operations of 1510 may be performedaccording to the methods described herein. In certain examples, aspectsof the operations of 1510 may be performed by a DFT-s-OFDM symbolmanager as described with reference to FIGS. 10 through 13.

At 1515 the UE 115 or a base station 105 may append a PTRS to thegenerated DFT-s-OFDM symbol. The operations of 1515 may be performedaccording to the methods described herein. In certain examples, aspectsof the operations of 1515 may be performed by a PTRS component asdescribed with reference to FIGS. 10 through 13. It is to be understoodthat the PTRS may alternatively be inserted into the DFT-s-OFDM symbolprior to the DFT spreading operation (e.g., as described with referenceto FIG. 6) without deviating from the scope of the present disclosure.

At 1520 the UE 115 or a base station 105 may transmit the generatedDFT-s-OFDM symbol comprising the cyclic prefix and the PTRS. Theoperations of 1520 may be performed according to the methods describedherein. In certain examples, aspects of the operations of 1520 may beperformed by a DFT-s-OFDM symbol manager as described with reference toFIGS. 10 through 13.

In some examples, aspects from two or more of the methods 1400 or 1500described with reference to FIG. 14 or 15 may be combined. It should benoted that the methods 1400 or 1500 are just example implementations,and that the operations of the methods 1400 or 1500 may be rearranged orotherwise modified such that other implementations are possible.

Techniques described herein may be used for various wirelesscommunications systems such as CDMA, TDMA, FDMA, OFDMA, single carrierfrequency division multiple access (DFT-s-OFDMA), and other systems. Theterms “system” and “network” are often used interchangeably. A CDMAsystem may implement a radio technology such as CDMA2000, UniversalTerrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95,and IS-856 standards. IS-2000 Releases may be commonly referred to asCDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM).

An OFDMA system may implement a radio technology such as Ultra MobileBroadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal MobileTelecommunications system (UMTS). 3GPP LTE and LTE-A are releases ofUMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM aredescribed in documents from the organization named “3rd GenerationPartnership Project” (3GPP). CDMA2000 and UMB are described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). The techniques described herein may be used for the systems andradio technologies mentioned above as well as other systems and radiotechnologies. While aspects an LTE system may be described for purposesof example, and LTE terminology may be used in much of the description,the techniques described herein are applicable beyond LTE applications.

In LTE/LTE-A networks, including such networks described herein, theterm eNB may be generally used to describe the base stations. Thewireless communications system or systems described herein may include aheterogeneous LTE/LTE-A network in which different types of eNBs providecoverage for various geographical regions. For example, each eNB or basestation may provide communication coverage for a macro cell, a smallcell, or other types of cell. The term “cell” may be used to describe abase station, a carrier or component carrier associated with a basestation, or a coverage area (e.g., sector) of a carrier or base station,depending on context.

Base stations may include or may be referred to by those skilled in theart as a base transceiver station, a radio base station, an accesspoint, a radio transceiver, a NodeB, eNB, Home NodeB, a Home eNodeB, orsome other suitable terminology. The geographic coverage area for a basestation may be divided into sectors making up only a portion of thecoverage area. The wireless communications system or systems describedherein may include base stations of different types (e.g., macro orsmall cell base stations). The UEs described herein may be able tocommunicate with various types of base stations and network equipmentincluding macro eNBs, small cell eNBs, relay base stations, and thelike. There may be overlapping geographic coverage areas for differenttechnologies.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell is alower-powered base station, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, shared)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs with service subscriptions with the networkprovider. A femto cell may also cover a small geographic area (e.g., ahome) and may provide restricted access by UEs having an associationwith the femto cell (e.g., UEs in a closed subscriber group (CSG), UEsfor users in the home, and the like). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a small cell may be referred toas a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB maysupport one or multiple (e.g., two, three, four, and the like) cells(e.g., component carriers). A UE may be able to communicate with varioustypes of base stations and network equipment including macro eNBs, smallcell eNBs, relay base stations, and the like.

The wireless communications system or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations may have similar frame timing, andtransmissions from different base stations may be approximately alignedin time. For asynchronous operation, the base stations may havedifferent frame timing, and transmissions from different base stationsmay not be aligned in time. The techniques described herein may be usedfor either synchronous or asynchronous operations.

The downlink transmissions described herein may also be called forwardlink transmissions while the uplink transmissions may also be calledreverse link transmissions. Each communication link describedherein—including, for example, wireless communications system 100 and200 of FIGS. 1 and 2—may include one or more carriers, where eachcarrier may be a signal made up of multiple sub-carriers (e.g., waveformsignals of different frequencies).

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. As used herein, including in the claims, the term “and/or,”when used in a list of two or more items, means that any one of thelisted items can be employed by itself, or any combination of two ormore of the listed items can be employed. For example, if a compositionis described as containing components A, B, and/or C, the compositioncan contain A alone; B alone; C alone; A and B in combination; A and Cin combination; B and C in combination; or A, B, and C in combination.

Also, as used herein, including in the claims, “or” as used in a list ofitems (for example, a list of items prefaced by a phrase such as “atleast one of” or “one or more of”) indicates an inclusive list suchthat, for example, a phrase referring to “at least one of” a list ofitems refers to any combination of those items, including singlemembers. As an example, “at least one of: A, B, or C” is intended tocover A, B, C, A-B, A-C, B-C, and A-B-C., as well as any combinationwith multiples of the same element (e.g., A-A, A-A-A, A-A-B, A-A-C,A-B-B, A-C-C, B-B, B-B-B, B-B-C, C-C, and C-C-C or any other ordering ofA, B, and C). Also, as used herein, the phrase “based on” shall not beconstrued as a reference to a closed set of conditions. For example, anexemplary operation that is described as “based on condition A” may bebased on both a condition A and a condition B without departing from thescope of the present disclosure. In other words, as used herein, thephrase “based on” shall be construed in the same manner as the phrase“based at least in part on.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media maycomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave are included in the definition of medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication, comprising:transmitting, via radio resource control (RRC) signaling, an indicationof a frequency corresponding to a direct current (DC) tone within a setof resource blocks.
 2. An apparatus for wireless communication,comprising: a processor, memory coupled with the processor; andinstructions stored in the memory and executable by the processor tocause the apparatus to: transmit, via radio resource control (RRC)signaling, an indication of a frequency corresponding to a directcurrent (DC) tone within a set of resource blocks.
 3. A non-transitorycomputer-readable medium storing code for wireless communication, thecode comprising instructions executable by a processor to: transmit, viaradio resource control (RRC) signaling, an indication of a frequencycorresponding to a direct current (DC) tone within a set of resourceblocks.
 4. A method for wireless communication, comprising: receiving,via radio resource control (RRC) signaling, an indication of a frequencycorresponding to a direct current (DC) tone within a set of resourceblocks.
 5. An apparatus for wireless communication, comprising: aprocessor, memory coupled with the processor; and instructions stored inthe memory and executable by the processor to cause the apparatus to:receive, via radio resource control (RRC) signaling, an indication of afrequency corresponding to a direct current (DC) tone within a set ofresource blocks.
 6. A non-transitory computer-readable medium storingcode for wireless communication, the code comprising instructionsexecutable by a processor to: receive, via radio resource control (RRC)signaling, an indication of a frequency corresponding to a directcurrent (DC) tone within a set of resource blocks.